Certain types of nonhydrolyzable siloxane-polyether copolymers are well known in the art and are readily available through many suppliers. These copolymers are manufactured by the coreaction of poly(dimethyl-siloxanes) containing SiH groups (hydrosiloxanes) with olefinic polyethers wherein the olefinic sites are allyl groups. The general reaction whereby these nonhydrolyzable linkages are created between silicone and polyether groups is: ##STR1##
However, the above reaction is not the sole reaction that is taking place during the preparation of the copolymer. It has been established that a significant percentage of the allyl groups are isomerized under the addition reaction conditions to give propenyl polyethers which do not participate in the hydrosilation reaction: ##STR2## See, for example, U.S. Pat. Nos. 3,507,923 and 3,836,560.
It has become common practice in the industry to use stoichiometric excesses (20 mole % or more) of the allyl polyethers to insure reaction of all the SiH groups. The excess unreacted allyl polyether or isomerized propenyl polyether are thus present as inert diluent, thereby reducing the potency or active concentration of the final copolymer.
Another competing undesirable reaction is that some of the SiH groups react with sources of hydroxy containing contaminants, or solvents containing hydroxy functionality such as water, methanol or ethanol. These act as SiH group scavengers and react in the following manner: ##STR3## This conversion of the SiH sites to SiOR sites acts to reduce the number of incorporated polyether moieties and it is known that the hydrogen gas released from this undesirable side reaction can be catalytically added across the double bond of the polyether. This reduces the effective concentration of olefinic polyether available for reaction. The overall effect is to reduce the molecular weight of the final copolymer. The reaction would look as follows: ##STR4##
Another source of concern is the HCl that is liberated when using hexachloroplatinic acid. It was clearly demonstrated by a group of French investigators that the hexachloroplatinic acid will liberate HCl as a by-product in the reaction system. This by-product is suspected to have a deleterious effect on the reaction system (for example, by inducing parallel protodesilylation reaction at the --C--Si-- main chain bonds). This is shown by G. deMarignan, D. Teysse, S. Boileau, J. Malthete and C. Noel, Polymer, 29, 1318 (1988).
It is shown by P. R. Dvornic and V. V. Gerov in Macromolecules, 27, 1068 (1994) that the use of neutral platinum-divinyldisiloxane complex Pt-DVDS!, also known as Karstedt catalyst, will give AB!n type molecules of increased molecular weight when compared to the use of hexachloroplatinic acid as catalyst. The use of Pt-DVDS enabled the synthesis of copolymers with a molecular weight of typically 30,000 daltons but in optimized conditions, 75,000 daltons. These compare to copolymers of molecular weight of the order of 1000-2000 daltons when using hexachloroplatinic acid. Although this is one method for obtaining increased molecular weight copolymers, the use of Pt-DVDS can result in the undesirable reaction of the DVDS into the backbone of the copolymer. This does not have an impact on the molecular weight obtained, but it could have a deleterious effect on how the copolymer performs in a particular application. For example, if this product was used in the manufacture of a polyurethane foam it would result in foam of inferior quality or, even worse, collapse the foam. The use of Pt-DVDS is also economically disadvantageous when compared to other hydrosilation catalysts.
U.S. Pat. No. 4,122,029 teaches the use of copolymers in the manufacture of emulsions for use in cosmetic applications. It is also stated,in U.S. Pat. No. 4,150,048 that high molecular weight non-hydrolyzable block copolymers may be useful in cosmetic applications. It is well known that products for use in cosmetic applications need to be of low odor, low color, free of toxic solvents, and of high molecular weight.
It is stated in U.S. Pat. No. 3,792,073 that linear siloxane-polyether copolymers of high molecular weight have very useful properties as surfactants for the preparation of mechanically frothed urethane foam and U.S. Pat. No. 3,793,237 shows their utility when used in open-celled rigid urethane foam. U.S. Pat. No. 4,150,048 states in column 3 that these desirable foam properties are derived from their high molecular weight. It also states that the desired degrees of polymerization (herein signified as (DP).sub.n)are 18 or higher. In that patent, the desired degrees of polymerization could only be obtained by using a heterogeneous platinum on carbon catalyst. If a homogeneous solution of hexachloroplatinic acid catalyst was used, the maximum degree of polymerization obtainable was 14.12. This corresponds to a maximum GPC average molecular weight (M.sub.w) of 56,000. These lower DP.sub.n and M.sub.w values are suggested to be caused by silicon-bonded hydrogen atoms being consumed in side reactions, such as with water inadvertently present in the system, or in the chloroplatinic acid in the hexahydrated form, or in other side reactions with protonic solvents such as methanol, ethanol, isopropanol or n-propanol. These low DP.sub.n and M.sub.w copolymers are not as active, and when the platinum on carbon catalyst is employed to obtain the higher molecular weight copolymers the resulting product suffers from the fact that the catalyst must be filtered to remove it from the product. The filtration process is a slow and expensive step due to the high viscosity of the final product and its propensity to foam during the filtration process. Even after filtration the product is reported to still possess a high color from residual unfilterable catalyst on carbon.
The current invention results in copolymers with a higher DP.sub.n and a high molecular weight. It will be shown herein that use of the described process results in copolymers with higher degrees of polymerization than were obtainable in U.S. Pat. No. 4,150,048 using the same ratio of reactants. It will further be shown that the resulting copolymer no longer requires the final filtration step and yields an improved color and low odor product. It will also be shown that this improved process can use the economically more advantageous hexachloroplatinic acid catalyst to give these results.